Magnetic recording media for longitudinal recording, process for producing the same and magnetic memory apparatus

ABSTRACT

A magnetic recording medium for longitudinal recording with a low media noise, a high S/N ratio and high reliabilities in corrosion resistance is disclosed. By making a magnetic layer from a Co-based alloy comprising 1 to 35 at. % of at least one element selected from the group consisting of Pt and Ir, 1 to 17 at. % of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W. Ge and Si, except for Si, whose concentration is 1 to 40 at. %, and 0.1 to 10 at. % of oxygen, a magnetic recording medium for longitudinal recording having an inplane coercivity of 1,200 Oe or more and a coercive squares of not more than 0.85 is obtained. 
     A process for producing the magnetic recording medium for longitudinal medium and a magnetic memory apparatus using the magnetic recording medium for longitudinal recording are also disclosed.

BACKGROUND OF THE INVENTION

This invention relates to magnetic recording media such as magneticrecording tapes, floppy disks, magnetic recording disks, etc., a processfor producing the same, and magnetic memory apparatuses using themagnetic recording media, and more particularly to magnetic recordingmedia for longitudinal recording suitable for high density magneticrecording, a process for producing the same and magnetic memoryapparatuses.

Heretofore, magnetic recording media using a metallic magnetic film havebeen proposed as magnetic recording media for longitudinal recording forhigh density magnetic recording, as disclosed in Japanese PatentPublication No. 54-33523. Processes for forming magnetic recording mediafor longitudinal recording include an evaporation process, a sputteringprocess, a plating process, an ion beam sputtering process, etc.

Recently, needs for higher density recording and higher reliability havebeen increased. For example, magnetic recording media for longitudinalrecording with a thin metallic magnetic film having an inplanecoercivity as high as about 700 Oe and a high corrosion resistance at ahigh temperature and a high humidity, such as thin metallic magneticfilm of magnetic alloy, e.g. Co-Pt, Co-Cr-Pt, Co-Ta-Pt, Co-Si-Pt,Co-Zr-Pt, Co-Hf-Pt, etc. have been proposed as in Japanese PatentApplications Kokai (Laid-open) Nos. 60-111323, 59-177725, 59-8806, etc.

Furthermore, it has been proposed to improve static magnetic propertiessuch as an inplane coercivity Hc, a squareness S, a coercive squarenessS*, etc. For example, it has been proposed to form a pure metal layer ofCr, Mo, W, Nh, W, etc. or an alloy layer of Cr-V, Cr-Fe, etc. as anunderlayer on a substrate and form a magnetic recording layer of Co-Ptalloy or Co-Cr-Pt alloy thereon, an disclosed in Japanese PatentApplication Kokai (Laid- open) No. 62-257617 (=U.S. Pat. No. 4,654,276),or to form a magnetic recording layer of Co-Cr-Pt alloy on a Ni-Punderlayer, as disclosed in Japanese Patent Application Kokai(Laid-open) No. 59-88806, or to form an alumite underlayer on asubstrate of aluminum alloy and form a magnetic recording layer ofcobalt (Co)-based alloy comprising 3 to 15 at. % of at least Mo, V andW, 3 to 20 at. % of Cr and 3 to 15 at. % of a noble metal element suchas Pt, Rh, Ru, Re, Pd, Ir, etc., the balance being at least 75 at. % ofCo, thereon, as disclosed in Japanese Patent Applications Kokai(Laid-open) Nos. 61-246917 and 61-253622.

Furthermore, Japanese Patent Application Kokai (Laid-open) No. 62-257617(=U.S. Pat. No. 4,654,276) and Japanese Patent Application Kokai(Laid-open) No. 62-257618 (=U.S. Pat. No. 4,652,499) disclose that whena magnetic recording layer of Co-Pt or Co-Cr-Pt is produced on anon-magnetic underlayer having a thickness of about 50 nm, such as Cr-Vunderlayer or W underlayer, the inplane coercivity Hc can be made higherthan 1,200 Oe and also the coercive squareness S* higher than 0.9.

SUMMARY OF THE INVENTION

The main object of the present invention is to improve the corrosionresistance of a metallic magnetic layer and also to increase the inplanecoercivity and the coercive squareness, thereby obtaining a higherdensity magnetic recording and a higher read output. Magnetic recordingmedia of the prior art generally have such a disadvantage that the medianoise tends to increase with a higher density magnetic recording and ahigher read output. Particularly with a recent higher density magneticrecording, the recording frequency has been increased and the band widthhas been broadened, and consequently the head noise and amplifier noisetend to increase. Thus, it has been desired to develop magneticrecording media having smaller noise characteristics than these noises,while maintaining a higher read output.

As the result of extensive studies, the present inventors have foundthat an increase in the inplane coercivity and coercive squareness canincrease the read and write characteristics at a higher density, butalso can increase the noise and thus is not always advantageous withrespect to the signal-to-noise ratio, and that particularly the noiseconsiderably increases when the coercive squareness is made more than0.9. Thus, in order to obtain magnetic recording media for longitudinalrecording with distinguished read and write characteristics, it isessential to satisfy these mutually contradicting magnetic properties atthe same time, and it is a current task to satisfy an inplane coercivityHc of not less than 1,200 Oe and a coercive squareness S* of not morethan 0.9, preferably not more than 0.85 at the same time. A coercivesquareness S* means a ratio of H to Hc (H/Hc) at a cross point of atangent line drawn at the point of inplane coercivity Hc in a magnetichysteresis loop with a straight line drawn at the point of remanencemagnetization Mr and in parallel to the magnetic field (H) axis.

A first object of the present invention is to provide magnetic recordingmedia for longitudinal recording with less noises, a distinguished S/Nratio and a high reliability in corrosion resistance, etc.

A second object of the present invention is to provide magneticrecording media for longitudinal recording with a high inplanecoercivity Hc, that is, at least 1,200 Oe and a small coercivesquareness S*, that is, not more than 0.9, preferably not more than0.85, which can read and write in a high S/N ratio even at a highdensity recording and has a high reliability, that is, high corrosionresistance and antiwear properties.

A third object of the present invention is to provide a process forproducing magnetic recording media for longitudinal recording that canattain the second object of the present invention.

A fourth object of the present invention is to provide magnetic memoryapparatuses using the magnetic recording media for longitudinalrecording that can attain the first or second object or both objects ofthe present invention.

The first object of the present invention can be attained by making amagnetic layer mainly from an alloy comprising Co, a material X composedof at least one element selected from the first group consisting of Cr,Mo and W, a material Y' composed of at least one element selected fromthe second group consisting of Ti, Zr, Hf, Ta, Nb, Ru and Rh, and amaterial Z composed of at least one element selected from the thirdgroup consisting of Al and Si. The alloy of the magnetic layer isrepresented by the following general formula:

    (Co.sub.1-a X.sub.a).sub.1-b-c Y'.sub.b Z.sub.c,

wherein it is desirable that a concentration of X on the basis of Co,that is, 100a, is 3 at. % to 20 at. % and concentrations of Y' and Z onthe basis of the sum total of Co and X, that is, 100b and 100c, are 1at. % to 15 at. % and 1 at. % to 15 at. %, respectively, where theconcentration of inevitable impurities is disregarded. Furthermore, itis desirable that the magnetic layer contains 0.1 at. % to 15 at. % ofoxygen.

Furthermore, it is particularly desirable with respect to an improvementof inplane coercivity to provide an intermediate layer of nonmagneticmaterial composed mainly of at least one of Cr, Mo and W, and theiralloys such as Cr-Ti, etc. between the magnetic layer and thenonmagnetic substrate. With magnetic recording media of the foregoingstructure, magnetic memory apparatuses of high capacity with a highreliability can be provided.

The effects of the magnetic layer of the foregoing structure can beobtained through the following functions. The functions of the presentinvention will be explained below, referring to use of a body centeredcubic (bcc) metal such as alloys composed mainly of at least one of Cr,Mo and W and their alloys such as Cr-Ti, etc. as an underlayer. On theunderlayer, the axis of magnetic anisotropy of Co is oriented to have aninplane anisotropic component so as to give a high inplane coercivity.Furthermore, by addition of at least 3 at. % of Cr, etc. to Co in themagnetic layer, a high inplane coercivity, for example, about 500 Oe orhigher, can be obtained. With increasing Cr concentration, the corrosionresistance of Co alloy increases, whereas the noise of Co alloydecreases. However, the saturation magnetization is abruptlydeteriorated with increasing Cr concentration, and thus more than 20 at.% of Cr to be added is not preferable.

In order to improve the saturation magnetization, the present inventorshave made extensive studies of additive elements and have found thataddition of Ti, Zr, Hf, V, Nb, Ta, Fe, Ru, Os, Rh, Ir, Pd, La, Sm, Pr,etc. can increase the saturation magnetization, but the media noise atthe read and write runs is large with these additive elements. That is,the saturation magnetization could be improved, whereas there appeared anew problem of an increase in the media noise. Thus, in order to reducethe media noise, the present inventors have also made extensive studiesof other additive elements, and have found that the media noise can bereduced by adding at least one element selected from the groupconsisting of Ti, Zr, Hf, Nb, Ta, Ru and Rh, that is, the aforementionedsecond group, used as additive elements for the improvement of thesaturation magnetization and also by adding at least one elementselected from the group consisting of Al and Si, that is, theaforementioned third group, thereto. Neither deterioration of corrosionresistance nor reduction in the saturation magnetization has beenobserved at all in that case.

In case of magnetic layers using materials X other than Cr, selectedfrom the aforementioned first group, the same function and effects as incase of Cr can be obtained.

The reduction in the media noise seems mainly due to the fact that analloy of material Y' selected from the second group and material Zselected from the third group segragates at the magnetic crystallinegrain boundary. That is, the alloy is nonmagnetic and thus the magneticinteraction (exchange coupling, magnetostatic coupling, etc.) is reducedamong the magnetic crystalline grains. As a result, the number ofcrystalline grains constituting the minimum unit region (cluster) ofmagnetization reversal is decreased, as compared with that of theconventional crystalline grains. (A possible minimum cluster is composedof a simple crystal grain.) Thus, the width of magnetic transitionregion as a cause for media noise is narrowed, resulting in reduction ofmedia noise. Particularly when a magnetic layer is formed so as tocontain 0.1 at. % to 15 at. % of oxygen, the magnetic crystalline grainsare made finer and the magnetic grain boundaries are made thicker and/ordenser to reduce the magnetic interaction much more. Thus, the medianoise is further reduced and the corrosion resistance is also improved.

The desirable concentrations of the additive elements can be explainedbelow. FIG. 2 shows media noise characteristics of magnetic recordingdisks prepared in the following manner, when subjected to read and writeruns with a Mn-Zn ferrite ring head with a gap length of 0.6 ∥m. Themagnetic disks were prepared by forming a Cr underlayer having athickness of 350 nm on an Al-Mg alloy substrate plated with Ni-P, 130 mmin diameter, a 25 magnetic layer of (Co₀.90 Cr₀.10)₀.96-c Ta₀.04 Al_(c)having a thickness of 70 nm and a C (carbon) protective layer having athickness of 40 nm successively thereon by RF magnetron sputtering at asubstrate temperature of 100° C. under an argon gas pressure of 15 mTorrwith an input power density of 1 W/cm². The relative head-to media speedis 15 m/sec and the recording frequency is 7 MHz. As shown in FIG. 2,the media noise is abruptly reduced with increasing Al concentration inthe magnetic layer, and its reduction is saturated around 10 at. % ofAl. Thus, even addition of more than 15 at. % of Al is less effectivefor the reduction of media noise. Furthermore, the saturationmagnetization and inplane coercivity are decreased with increasing Alconcentration, resulting in a decrease in the read output.

On the other hand, reduction in the total noise N_(T) of magneticrecording system is only about 20%, when a MnZn ferrite ring head or ametal-in-gap type lead (MIG head) is used as a head and even when themedia noise is reduced to 4 μVrms from 7 μVrms. Thus, addition of atleast 1 at. % of Al is satisfactory and addition of 2.5 at. % or more ofAl is more preferable for remarkable reduction of the media noise.Similar effects are obtained in case of addition of Si or Al-Si alloy inplace of Al.

The reason why there is no significant difference in the total noise ofa magnetic recording system between the media noise of 7 μVrms and thatof 4 μVrms is explained as follows:

The total noise N_(T) of the system is a function of media noise N and ahead amplifier noise N_(HA) and can be represented by the followingequation (1): ##EQU1##

When a MnZn ferrite ring head or a metal-in-gap type head is used as ahead, the head amphifier noise N_(HA) becomes a constant of about 7μVrms.

Thus, the equation (1) will be as follows: ##EQU2##

Thus, when N is decreased to 4 μVrms from 7 μVrms, N_(T) will be reducedby about 20%.

Corrosion resistance of C/(Co₀.89 Cr₀.11)₀.95-b Zr_(b) Si₀.05 /Cr mediaprepared under the same conditions as above was evaluated by atemperature/humidity corrosion test at 70° C. and 85% RH, and it wasfound that at 1 at. % or more of Zr no read and write error wasobservable even after 3 weeks, and a good corrosion resistance could beobtained, whereas above 15 at. % of Zr, deterioration of saturationmagnetization and inplane coercivity was remarkable and no high readoutput was obtained. At 1 to 15 at. % of Zr, Hc was high, i.e. 700 Oe ormore. Similar effects were obtained with Ti, Hf, Nb, Ta, Ru and Rh ortheir alloys in place of Zr.

By allowing an Ar gas to contain 0.02 vol. % to 1.0 vol. % of oxygenwhen the magnetic layer of foregoing composition is formed, the magneticlayer can contain 0.1 at. % to 15 at. % of oxygen. In that case, themagnetic crystalline grains are made finer with increasing concentrationof oxygen and also the oxide segragates at the grain boundary, resultingin reduction of the aforementioned magnetic interaction and improvementof the corrosion resistance.

It is needless to say that a magnetic memory apparatus of larger memorycapacity with a high reliability can be provided when a magneticrecording disk, a floppy disk or a magnetic recording tape of theforegoing structure is used.

Furthermore, the first object of the present invention can be alsoattained by making a magnetic layer mainly from an alloy containing Coand Pt and further containing a material X composed of at least oneelement selected from the first group consisting of Ni, Cr, Mo and W, amaterial Y' composed of at least one element selected from the secondgroup consisting of Ti, Zr, Hf, Ta, Nb, Ru and Rh and a material Zcomposed of at least one element selected from the third groupconsisting of Al and Si.

The alloy of the magnetic layer can be represented by any one of thefollowing general formulae:

    (Co.sub.1-a Ni.sub.a).sub.1-b-c-d Y'.sub.b Z.sub.c Pt.sub.d'

    (Co.sub.1-a' B'.sub.a').sub.1-b-c-d Y'.sub.b Z.sub.c Pt.sub.d' or

    (Co.sub.1-a-e Ni.sub.a B'.sub.e).sub.1-b-c-d Y'.sub.b Z.sub.c Pt.sub.d'

where it is desirable that a concentration, 100d, of Pt is 0.1 at. % to30 at. %, a concentration, 100c, of material Z is 1 at. % to 15 at. %,and a concentration, 100b, of material Y' is 1 at. % to 15 at. %, thebalance being Co and X. B' is a material composed of at least oneelement selected from the group consisting of Cr, Mo and W. It isdesirable that a is 0.1 to 0.5, a' is 0.01 to 0.2 and e is 0.01 to 0.15,where the concentration of inevitable impurity is disregarded. It isfurther desirable with respect to the reduction of media noise that themagnetic layer contains 0.1 at. % to 15 at. % of oxygen, and it is alsopreferable with respect of an improvement of inplane coercivity toprovide an intermediate layer of non-magnetic material composed mainlyof at least one of Cr, Mo and W, and their alloys such as Cr-Ti, etc.between the magnetic layer and the nonmagnetic substrate. With magneticrecording media of the foregoing structure, magnetic memory apparatusesof high reliability suitable for a high density magnetic recording canbe provided.

The effects of the magnetic layer of the foregoing structure can beobtained through the following functions. The functions of the presentinvention will be explained below, referring to use of a body centeredcubic (bcc) metal such as alloys composed mainly of at least one of Cr,Mo and W and their alloys such as Cr-Ti, etc. as an underlayer. On theunderlayer, the Co layer is grown so that the axis of magneticanisotropy of Co is oriented to have an inplane anisotropic componentand thus to give a high inplane coercivity. Furthermore, by addition ofNi, Cr, Mo, W, Pt, etc. to Co in the magnetic layer, a higher inplanecoercivity, for example, about 500 Oe or higher, can be obtained.

As a result of further studies, the present inventors have found that byaddition of Pt and at least one element selected from the first groupconsisting of Ni, Cr, Mo and W to Co, a higher inplane coercivity, anappropriately high saturation magnetization and a high read output canbe obtained, but that these alloy still have problems of large medianoise and poor corrosion resistance. Thus, the present inventors havefurther studied addition of various elements of groups 4a, 5a, 6a, 8, 8band 4b of the periodic table to the alloys composed of Co, Pt and thematerial selected from the first group, such as CoNiPt, CoCrPt,CoNiCrPt, etc. to reduce the media noise and improve the corrosionresistance while maintaining a high inplane coercivity, and have foundthat the material composed of at least one element selected from thethird group consisting of Al and Si, as added, segregates at themagnetic crystalline boundary of a magnetic layer containing Co as themain component to reduce the magnetic interaction among the magneticcrystalline grains, thereby considerably reducing the media noise.However, it has been found that the corrosion resistance is notimproved, but rather deteriorated, because it seems that the segregatesat the magnetic crystalline grain boundary cause to more easily formlocal cells between the magnetic crystalline grains and the grainboundary. In order to solve this problem, the present inventors havestudied further addition of elements of groups 4a, 5a, 6a, 8, 3b, 4b,etc. of the periodic table. As a result of evaluation of the corrosionresistance by a NaCl spray test, it has been found that the corrosionresistance can be considerably improved without any deterioration ofmedia noise by further addition of a material composed of at least oneelement selected from the second group consisting of Ti, Zr, Hf, Ta, Nb,Ru and Rh, because elements of Ti, Zr, Hf, Ta, Nb, etc. form a densepassivation film at the grain boundary or elements of Ru, Rh, etc. makethe oxidation-reduction potential of the magnetic crystalline grainsnobler without the increase of magnetic interactions among the grains.It has been further found that the highest corrosion resistance can beobtained without much deterioration of media noise by addition of analloy composed of elements selected from these two groups to give thesetwo effects. As far as the corrosion resistance is concerned, thecorrosion resistance can be improved by adding Pd, Pr, etc., forexample, to a CoNiPtSi-based alloy, but the media noise is increasedthereby.

The concentrations of the aforementioned additive elements will beexplained below. FIG. 3 shows a dependence of inplane coercivity on Niconcentration of magnetic recording disks prepared in the followingmanner. A Cr underlayer having a thickness of 420 nm is formed on anAl-Mg alloy substrate plated with Ni-P, 51/4" in diameter, and amagnetic layer of (Co_(1-a) Ni_(a))₀.85 Pt₀.05 Si₀.05 Zr₀.05 having athickness of 60 nm is formed thereon by RF magnetic sputtering at asubstrate temperature of 100° C. under an argon gas pressure of 15 mTorrwith an input power density of 1.5 W/cm². It is obvious from FIG. 3 thatat a Ni concentration 100a of 10 at. % to 60 at. % on the basis of Co, ahigh inplane coercivity, that is, 700 Oe or higher, can be obtained.

In case of magnetic recording media of (Co_(1-a') Cr_(a'))₀.85 Pt₀.05Si₀.05 Ta₀.05 /Cr prepared in the same manner as above, a high inplanecoercivity, that is, 700 Oe or higher, can be obtained at a Crconcentration 100a' of 3 at. % to 20 at. % on the basis of Co.

In case of magnetic recording media of (Co )_(1-a-e) Ni_(a) Cr_(e))₀.85Pt₀.05 Al₀.05 Zr₀.05 /Cr prepared under the same conditions as above, ahigh inplance coercivity, that is, 700 Oe or higher, can be obtained inranges of 0.1 ≦a≦0.5 and 0.01 ≦e≦0.15.

The same effects can be also obtained with Mo or W in place of Cr orwith Ti, Hf, Nb, Ru, Rh or their alloys in place of Ta and Zr asadditive elements to the magnetic layer.

FIG. 4 shows a dependence of the inplane coercivity of magneticrecording media of (Co₀.7 Ni₀.3)₀.9-d Pt_(d) Al₀.05 Zr₀.05 /Cr preparedunder the same conditions as above upon a Pt concentration d. Aparticularly high inplane coercivity, that is, 1,000 Oe or higher, canbe obtained with a high read output at a Pt concentration 100d of 0.1at. % to 20 at. %, preferably 2 at. % to 10 at. %.

FIG. 5 shows a result of evaluation of read and write characteristics ofmagnetic recording disks comprising a magnetic layer of (Co₀.7Ni₀.3)₀.9-c Zr₀.05 Si_(c) Pt₀.05 having a thickness of 60 nm, a carbon(C) protective layer having a thickness of 40 nm formed thereon underthe same conditions as above, and a layer of highly fluorinated liquidlubricant of perfluoroalkylpolyether by means of a Mn-Zn ferrite ringhead. As shown in FIG. 5, the media noise is abruptly decreased withincreasing Si concentration, and its decrease is saturated around 10 at.% of Si. Thus, addition of more than 15 at. % of Si is less effectivefor the reduction of media noise. Furthermore, the saturation magneticflux density and the inplane coercivity are abruptly decreased withincreasing Si concentration, resulting in a decrease in the read output.

On the other hand it is obvious therefrom that the effect on thereduction of media noise is remarkable at a Si concentration of 1 at. %or higher, preferably 3 at. % or higher in the same manner as above. Thesame effect is also observable in case of adding Al or an alloy of Aland Si.

Magnetic recording media of C/(Co₀.6 Ni₀.4)₀.9-b Zr_(b) Al₀.05 Pt₀.05/Cr were prepared under the same conditions as above, and theircorrosion resistance was evaluated by a NaCl spray test. It was foundthat the corrosion resistance could be improved 5-fold or more withoutany deterioration of media noise by selecting a Zr concentration 100b of1 at. % or more. Addition of more than 15 at. % of Zr was not desirablebecause the saturation magnetic flux density and the inplane coercivitywere considerably lowered, resulting in a decrease in the read output.An inplane coercivity of 700 Oe or more could be obtained at a Zrconcentration of 1 at. % to 15 at. %. The same effect could be alsoobtained with Ti, Hf, Ta, Nb, Ru, Rh and their alloys in place of Zr.

By allowing the Ar gas to contain 0.05 vol. % to 2 vol. % of oxygen whena magnetic layer is formed from the magnetic materials of the foregoingcomposition, the magnetic layer can contain 0.1 at. % to 15 at. % ofoxygen, and the magnetic crystalline grains can be made fine withincreasing concentration of oxygen and the oxide segregates at the grainboundary to reduce the magnetic interaction among the magneticcrystalline grains, thereby further reducing the media noise. At thesame time, the strength of film surface passivation layer can beincreased at the same time and thus the corrosion resistance can beimproved.

With magnetic recording disks, floppy disks or magnetic recording tapesof the foregoing structure in combination with a magnetic head such as aMnZn ferrite ring head or a metal-in-gap type head, a magnetic memoryapparatus with distinguished read and write characteristics and a highreliability can be provided.

The second object of the present invention can be attained by magneticrecording media for longitudinal recording, which comprises anonmagnetic substrate, a nonmagnetic metallic underlayer comprising atleast one metal element selected from the group consisting of Cr, Mo, W,V, Nb and Ta formed on the nonmagnetic substrate and a magnetic layer ofCo-based alloy formed on the nonmagnetic metallic underlayer, theCo-based alloy comprising 1 to 35 at. % of at least one first additiveelement selected from the group consisting of Pt and Ir, 1 to 17 at. %,preferably 3 to 15 at. %, of at least one second additive elementselected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W,Ge and Si, except for Si, whose concentration is 1 to 40 at. %,preferably 2 to 30 at. %, and 0.1 to 10 at. % of oxygen, sum total ofthe first and second additive element and oxygen being 2.2 to 50 at. %,the balance being Co. As shown in FIG. 8, the thickness of thenonmagnetic metal underlayer is preferably 150 nm or more, and morepreferably 200 nm or more with respect to an improvement of inplanecoercivity. When the magnetic layer is formed on the metallicunderlayer, the inplane components of crystalline orientation of themagnetic layer can be increased, which can improve the inplanecoercivity.

When the thickness of the nonmagnetic metallic underlayer exceeds 600nm, a problem of surface roughness is serious, and the flyability of amagnetic head is deteriorated. A larger thickness also results in ahigher cost. Thus, it is desirable that the film thickness of anonmagnetic metallic underlayer is not more than 600 nm. More preferableconcentrations of the magnetic layer of Co-based alloy are 3 to 13 at.%, preferably 5 to 9 at. %, of the first additive element and 3 to 15at. % of the second additive element, except for Si, whose concentrationis 2 to 30 at. %.

The second additive elements will be further explained below: It isparticularly preferable to select Cr, Mo, W, Ge and Si from the groupand it is also desirable that at least one of these elements iscontained as an essential additive component. That is, when the secondadditive elements are classified into group A consisting of Cr, Mo, W,Ge and Si and group B consisting of Ti, Zr, Hf, V, Nb and Ta, at leastone element selected from the group A and at least one element selectedfrom the group B must be contained at the same time, or at least oneelement selected from the group A must be contained as an essentialcomponent. A preferable concentration of the additive element from thegroup A is 3 to 15 at. %, as described above, except for Si, whoseconcentration is 2 to 30 at. %, and a preferable concentration of theadditive element from the group B is 1 to 15 at. %.

The nonmagnetic metallic underlayer can be composed of at least onemetal element selected from the group consisting of Cr, Mo, W, V, Nb andTa and at least one element selected from the group consisting of Ti,Si, Ge, Cu, Pt, Rh, Ru, Re, Pd and oxygen, where a preferableconcentration of at least one element selected from the group consistingof Ti, Si, Ge and Cu is 1 to 30 at. %, a preferable concentration of atleast one element selected from the group consisting of Pt, Rh, Ru, Reand Pd is 0.01 to 10 at. % and a preferable concentration of oxygen is0.1 to 10 at. %.

Such characteristics as an inplane coercive sequareness S* of not morethan 0.95, preferably 0.85 to 0.4, more preferably 0.81 to 0.6 and aninplane coercivity Hc of not less than 1,200 Oe, preferably at least1,500 Oe, can be obtained thereby, and a magnetic layer withdistinguished corrosion resistance and S/N ratio can be obtained.Furthermore, addition of an appropriate amount of Ni, Al, etc. to themagnetic layer of Co-based alloy can improve the S/N ratio, though thecorrosion resistance is deteriorated.

The third object of the present invention can be attained by a processfor producing magnetic recording media for longitudinal recording, whichcomprises a step of forming a nonmagnetic metallic underlayer comprisingat least one metal element selected from the group consisting of Cr, Mo,W, V, Nb and Ta on a nonmagnetic substrate by physical vapor deposition,a step of forming on the underlayer a magnetic layer of Co-based alloycomprising 1 to 35 at. % of at least one first additive element selectedfrom the group consisting of Pt and Ir, 1 to 17 at. %, preferably 3 to15 at. %, of at least one second additive element selected from thegroup consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ge and Si, exceptfor Si, whose concentration is 1 to 40 at. %, preferably 2 to 30 at. %,and 0.1 to 10 at. % of oxygen, total of the first and second additiveelements and oxygen being 2.2 to 50 at. %, the balance being Co, in aninert gas containing a very small amount of oxygen by sputtering of atarget containing the first and second additive elements, and a step offorming on the magnetic layer a protective layer. It is preferable toprovide a step of forming an underlayer of nonmagnetic plating film suchas a Ni-P plating film, etc. in advance to the step of forming thenonmagnetic metallic underlayer. The nonmagnetic metallic underlayer andthe magnetic layer of Co-based alloy can be formed by sputtering, vapordeposition, plating, ion beam deposition, etc. Particularly, DCmagnetron sputtering is preferable in respect to the deposition rate andlayer quality control.

The nonmagnetic metallic underlayer comprising at least one metalelement selected from the group consisting of Cr, Mo, W, V, Nb and Ta tobe formed on the nonmagnetic substrate by physical vapor deposition cancontain at least one element selected from the group consisting of Ti,Si, Ge, Cu, Pt, Rh, Ru, Re, Pd and oxygen as a secondary component. Inthat case, a preferable concentration of at least one element selectedfrom the group consisting of Ti, Si, Ge and Cu is 1 to 30 at. %, apreferable concentration of at least one element selected from the groupconsisting of Pt, Rh, Ru, Re and Pd is 0.01 to 10 at. %, and apreferable concentration of oxygen is 0.1 to 10 at. %.

Furthermore, it is preferable to form a magnetic layer of Co-based alloycontaining 3 to 13 at. %, preferably 5 to 9 at. %, of the first additiveelement and 3 to 15 at. % of the second additive element, except for Si,whose concentration is 2 to 30 at. %.

The second additive element will be further explained below. It isparticularly preferable to select Cr, Mo, W, Ge and Si from the groupand it is desirable to contain at least one of these elements as anessential component. That is, when the second additive elements areclassified into group A consisting of Cr, Mo, W, Ge and Si and group Bconsisting of Ti, Zr, Hf, V, Nb and Ta, at least one element selectedfrom the group A and at least one element selected from the group B mustbe contained at the same time, or at least one element selected from thegroup A must be contained as an essential component. A preferableconcentration of the element of group A is 3 to 15 at. % except for Si,whose concentration is 2 to 30 at. %, and a preferable concentration ofthe element of group B is 1 to 15 at. %, as mentioned before. A magneticlayer must be formed under sputtering conditions that can satisfy theforegoing concentrations.

It is desirable to form a magnetic layer by sputtering, whilemaintaining the underlayer substrate in a heated state, which ispractically preferably at 100° to 350° C. Above 350° C., the underlayersubstrate will react with the magnetic layer, whereas at a temperaturebelow 100° C. intermetallic compounds are easy to form, and the coercivesquareness becomes abnormally larger. It is preferable to chemicallyand/or physically roughen the surface of a substrate (grooves,irregularities or scars) by an etching and/or abrasing treatment, forexample, generally called "texturing treatment" in advance as apreliminary step for forming a magnetic layer. For example, by makingfine grooves, irregularities or scars, 2 nm to 30 nm in terms ofcenterline average roughness on a disk substrate in the moving directionof a magnetic head, the crystalline grains of the nonmagnetic metallicunderlayer on the disk substrate surface and the magnetic layer formedthereon undergo crystalline orientation particularly in the movingdirection of the magnetic head, whereby magnetic properties such assquareness, inplane coercivity, etc. in the moving direction of themagnetic head ca be considerably improved. The texturing treatment cancontribute to an improvement of magnetic properties in accordance withthe substrate heating when a magnetic layer is formed. Particularly, thedisks with surface irregularities and/or scars are preferable to showmuch improved CSS (contact-start/stop) characteristic.

The reasons why the second and third objects of the present inventioncan be attained will be explained in detail below:

The nonmagnetic metallic underlayer of pure metal or an alloy comprisingat least one metal element selected from the group consisting of Cr, Mo,W, V, Nb and Ta, provided on the nonmagnetic substrate, gives a largeinfluence on the crystallographic orientation and the magneticproperties of a magnetic layer of Co-based alloy to be formed on thesurface of the nonmagnetic metallic underlayer. That is, theabove-mentioned nonmagnetic metallic underlayer has a body-centeredcubic structure and is liable to have a (110) orientation on thenonmagnetic substrate. The magnetic layer to be formed thereon easilyundergoes epitaxial growth and thus has more inplane components ofmagnetic anisotropy. Thus, the nonmagnetic metallic underlayer acts toincrease the inplane coercivity Hc of the magnetic layer.

FIG. 13A and FIG. 13B show X-ray diffraction pattern of magneticrecording media for longitudinal recording and the crystallographicorientation and the crystallinity of magnetic layers and underlayersaccording to embodiments of the present invention, respectively. Thatis, a CrTi alloy underlayer with various Ti concentrations of 1 to 30at. % having a thickness of 10 to 500 nm, a magnetic layer of Co-15 at.% Cr-8 at. % Pt-1 at. % Si having a thickness of 50 nm, and a Cprotective layer having a thickness of 30 nm were formed on astrengthened glass substrate, 3.5" in diameter, in succession by DCsputtering in a Ar gas atmosphere containing 0.1 vol. % of oxygen at asubstrate temperature of 110° C under a gas pressure of 10 mTorr with aninput power density of 1 W/cm².

As shown in FIG. 13B, CrTi mainly takes a (100) orientation when theCrTi underlayer has a thickness of less than 0.05 μm, and the componentof (110) orientation will abruptly increase when the CrTi underlayerthickness exceeds 0.15 μm (150 nm) and the CoCrPtSi magnetic layer willalso epitaxially grow and take a (1011) orientation with the inplanec-axis component. Here, c-axis is the principal axis of the magneticanisotropy of CoCrPtSi. By providing a CrTi underlayer, the (1010)orientation, where the c-axis exists in the plane, will also develop atthe same time. Thus, by providing a CrTi underlayer, the (1011) and(1010) orientations, where the c-axis of CoCrPtSi has inplanecomponents, are developed, resulting in a higher inplane coercivity. Inthat case, the magnetic layer has an oxygen concentration of 2 at. %.

Relationships shown in FIGS. 13A and 13B are not limited to CoCrPtSi andCrTi, and also hold valid in other embodiments of the present invention.

The thickness of the nonmagnetic metallic underlayer also plays animportant role to control not only the inplane coercivity Hc, but alsothe coercive squareness S*, as will be explained, referring to FIG. 8.

FIG. 8 is a diagram of characteristic curve showing relationshipsbetween the thickness of non-magnetic metallic underlayer and themagnetic properties Hc and S* of magnetic recording media prepared byforming an Ni-P plating layer on a nonmagnetic Al-Mg alloy disksubstrate by a known method, and then forming a nonmagnetic metallicunderlayer (exemplified by Cr in this case) and a magnetic layer(exemplified by Co₈₀ Cr₁₀ Pt₁₀ in this case) of the present inventionthereon in succession at a substrate temperature of 150° C., where thethickness of the magnetic layer of the magnetic recording media is madeconstant to 75 nm. Here 2 at. % of oxygen is contained in the magneticlayer.

As is obvious from FIG. 8, a remarkable abrupt change is observablearound an underlayer thickness of 150 nm, that is, the implanecoercivity Hc exceeds 1,200 Oe in the region where the inplane coercivesquareness S* is lower than 0.85, and when the underlayer thicknessexceeds 200 nm, S* becomes less than 0.8 and Hc becomes exceeds 1,500Oe, resulting in a higher recording density and in a higher S/N ratio.That is, an increased underlayer thickness can improve the crystallineorientation of underlayer and thus can drastically improve the magneticproperties. In this manner, the overall strength of the layers incombination is improved and thus the antiwear properties are alsoimproved. However, when the underlayer thickness exceeds 600 nm, thenonmagnetic metal that forms the underlayer is liable to grow abnormallyand the roughness of magnetic layer surface is increased. That is, themagnetic layer surface becomes coarser and the magnetic head flyabilitywill be deteriorated. The production cost will also be higher in thiscase. Thus, it is desirable that the underlayer thickness is not morethan 600 nm. That is, a practically preferable thickness of nonmagneticmetallic underlayer is 150 to 600 nm, more preferably 200 to 450 nm.

Relationships between the inplane coercive squareness S* and the medianoise of magnetic recording media are shown by a characteristic curve inFIG. 11. When S* exceeds 0.85, the media noise abruptly increases,whereas when S* becomes less than 0.4, the read output waveform will bedeformed. Thus, a practical S* is 0.85 to 0.4, preferably 0.81 to 0.5,more preferably 0.75 to 0.6.

When the nonmagnetic metallic underlayer of Cr, Mo, W, etc. contains 0.1to 10 at. % of oxygen, the crystalline grains in the magnetic layer,which epitaxially grows thereon, will have grain sizes of not more than100 nm, resulting in a decrease in the media noise. Thus, this isparticularly preferable. However, when the oxygen concentration of theunderlayer exceeds 10 at. %, the epitaxial growth is considerablysuppressed and the inplane coercivity will be deteriorated.

Furthermore, at least one element selected from the group consisting ofTi, Si, Ge, Cu, Pt, Ru, Rh, Re and Pd to be contained in the nonmagneticmetallic underlayer can make the crystalline grains of the underlayerfiner as in the case of oxygen as contained, and can also make thecoercive squareness of a magnetic layer to be formed thereon not morethan 0.85, resulting in a decrease in the media noise. In this case, asshown in FIG. 13A and FIG. 13B, the crystalline orientation of theunderlayer will be increased, and as shown in FIG. 15 the effect uponthe inplane coercivity and the read output is also increased. Thus, thisis particularly preferable. Practically preferable concentrations ofthese elements are 1 to 30 at. % for at least one element selected fromthe group consisting of Ti, Si, Ge and Cu and 0.01 to 10 at. % for atleast one element selected from the group consisting of Pt, Ru, Rh, Reand Pd. A lower concentration will make the effect unsatisfactory,whereas a higher concentration will suppress the epitaxial growth,deteriorate the inplane coercivity or excessively increase the S*,resulting in deterioration of the read and write characteristics. Thus,a lower or higher concentration is not desirable.

It is particularly preferable to treat the substrate underlayer surfaceof Ni-P, etc. to have fine scars and/or grooves substantially in thehead moving direction as a preliminary step before the formation of anonmagnetic metallic underlayer to make a centerline average roughnessRa of 1 to 10 nm in the head moving direction and 2 to 30 nm in thedirection perpendicular to the head moving direction, whereby theinplane coercivity can be made higher in the head moving direction thanin the radial direction and also the read output can be made higher byone tenth to two tenths. Thus, this is particularly preferable and isdue to the so called graphoepitoxial effect that a nonmagnetic metallicunderlayer develops in accordance with the shape of the substrateunderlayer, as clarified by observation with SEM, etc. When Ra in theradial direction is not more than 2 nm, the effect is smaller, whereaswhen it is more than 30 nm, the antiwear properties will bedeteriorated.

Relationships between the concentrations of magnetic layer of Co-basedalloy and the magnetic properties will be explained below.

The role of 1 to 35 at. % of at least one first additive elementselected from the group consisting of Pt and Ir to be contained in acomposition containing Co as the main component is principally toincrease the inplane coercivity. However, this role can be playedthrough an interaction in the presence of 1 to 17 at. %, preferably 3 to15 at. % of at least one second additive element selected from the groupconsisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ge and Si, except forSi, whose concentration is 1 to 40 at. %, preferably 2 to 30 at. %, and0.1 to 10 at. % of oxygen, as in the case of the inplane corecivesquareness S*, and the role is not played through the single action ofthe individual first additive elements for the following facts gatheredby the present inventors from the following experimental results. Ahigher inplane coercivity can be easily obtained by adding only thefirst additive element (Pt and Ir) to Co, but it is difficult to stablyobtain a high coercivity of 1,000 Oe or more only through suchcombinations as above, and furthermore the media noise is higher and ahigher S/N ratio is hard to obtain. The present inventors have foundthat magnetic recording media with higher inplane coercivity Hc andcrystalline orientation and a higher S/N ratio even at a high densityrecording can be obtained by adding the first additive element and thesecond additive element to Co and making a magnetic layer therefrom in adischarge gas atmosphere containing oxygen. When Co contains the secondadditive element and when the discharge gas atmosphere such as Ar, etc.contain an oxygen gas at the formation of a magnetic layer bysputtering, the second additive element segregates at the grain boundaryand in the grains with the help of the oxygen to reduce the magneticinteraction among the magnetic crystalline grains and improve thecrystalline orientation, and consequently the media noise of magneticrecording media will be reduced. When only the second additive elementis added to Co without the first additive element, the inplanecoercivity Hc is decreased, and thus the read output is liable todecrease. When the first additive element and the second additiveelement are added to Co at the same time as in the present invention,the inplane coercivity Hc is also increased, as shown in FIG. 16, andthus the media noise is lower than that in the case of only addition ofthe first additive element (Pt and Ir) to Co. Thus, a higher S/N ratiocan be obtained as a result. The magnetic recording media shown in FIG.16 has a magnetic layer of Co-15 at. % Cr-7 at. % Pt-3 at. % Si having athickness of 65 nm, a Cr underlayer having a thickness of 350 nm and a Cprotective layer having a thickness of 40 nm. In this case, it isdesirable that the magnetic layer has an oxygen concentration of 0.1 at.% or more. When the oxygen concentration of the magnetic layer exceeds10 at. %, the oxidation considerably proceeds, and the saturationmagnetization and the inplane coercivity are also lowered, resulting ina considerable decrease in the read output. Thus, a practicallypreferable oxygen concentration is 0.1 to 10 at. %. The oxygenconcentration of the magnetic layer can be adjusted to a desired valuein case of making the layer, for example, by sputtering while adjustingthe oxygen partial pressure in the discharge gas atmosphere of Ar, etc.

In the foregoing, functions and the effective concentrations of theadditive elements have been explained, and it is desirable that the sumtotal of the additive elements including the oxygen is 50 at. % at most,that is, Co as the main component that constitutes the balance has aconcentration of at least 50 at. %.

The foregoing functions will be further explained below from thecrystallographic viewpoint.

When a magnetic layer is formed on a nonmagnetic substrate through anonmagnetic metallic underlayer by sputtering in an Ar gas containing0.1 vol. % of oxygen, as explained before, an inplane coercivity Hc of1,200 Oe or more can be obtained at a concentration of the firstadditive element (exemplified by Pt) of 1 to 35 at. %, as shown in FIG.6. By adding Pt to Co, a Co-Pt ordered plase appears in the crystallinegrains to suppress the movement of magnetic domain boundary. The inplanecoercivity becomes maximum at a Pt concentration of 13 at. %. Inconnection to the appearance of Co-Pt ordered plase, the mechanism ofthe development of inplane coercivity is different between a magneticlayer having a Pt concentration of more than 13 at. % and a magneticlayer having a Pt concentration of less than 13 at. %, and particularlya dynamic magnetization reversal takes place smoothly at a Ptconcentration of less than 13 at. %. Correspondingly, magnetic recordingmedia having a Pt concentration of less than 13 at. % have particularlyhigh overwrite characteristics and have a high efficiency of leakagerecording in the track width direction, a high efficiency of erase andan effect of broad margin for a position error at the read and writeruns with a magnetic recording head. The effect is particularlyremarkable at a Pt concentration of 9 at. % or less. Thus, a preferablePt concentration is less than 13 at. %, more preferably, 9 at. % orless. With increasing Pt concentration, the saturation magnetization isslowly decreased. That is, there is such a tendency that the saturationmagnetization will be decreased and the media noise will be relativelyincreased at a Pt concentration of 3 at. % or more, and, as show in FIG.9 the S/N ratio becomes particularly high at a Pt concentration of 1 to3 at. %. Furthermore, Pt and Ir are expensive noble metals, and additionof these metals in an unnecessarily large amount is not preferable withrespect to cost. A practically more preferable concentration of Pt is 1to 3 at. %, as described above. When the concentration of the firstadditive element such as Pt is more than 3 at. %, it is desirable toimprove the overwrite characteristics by making a concentration of Ptand Ir less than 13 at. %, preferably 9 at. % or less, as describedabove, and also to improve the corrosion resistance by making aconcentration of Co less than 75 at. % to considerably reduce the medianoise, resulting in an increase in the S/N ratio. As the second additiveelement to be added to Co together with the first additive element suchas Pt, a group of Ge and Si are particularly desirable besides Cr, Moand W as shown in FIG. 6, and it is needless to say that other elementsof the group, i.e. Ti, Zr, Hf, V, Nb and Ta are also effective.Particularly, in case of quaternary magnetic alloys containing the otherelements of the group, oxides or hydroxides of these elementspredominantly segregate on the surface or at the crystalline grainboundary to considerably improve the corrosion resistance, as comparedwith the ternary alloys, as shown in FIG. 12. Thus, the quaternarymagnetic alloys are particularly preferable. FIG. 12 shows a relativemagnetization Ms(t)/Ms(o) indicating a degree of deterioration due tocorrosion on the ordinate and time (hr) of NaCl spray test at 40° C. onthe abscissa, and shows that the magnetic layers maintaining a relativemagnetization of initial level for a longer time have a good corrosionresistance. Magnetic layers of Co-20 at. % Si-8 at. % Pt, Co-10 at. %Ge-8 at. % Pt and Co-8 at. % Pt (comparative) likewise formed haverelative magnetizations of 0.85, 0.82 and 0.75, respectively, 4 hoursafter the NaCl spray test.

In the quaternary magnetic alloys of the present invention, Ti, Zr, Hf,V, Nb, Ta, etc. segregate at the crystalline grain boundary and in thecrystalline grains owing to the synergistic effect of Cr, Mo, etc. toreduce the magnetic interaction among the crystalline grains and improvethe read and write characteristics, as described before, and thus thequaternary magnetic alloys are more desirable than the ternary magneticalloys of CoPt containing one of Cr, Mo, W, Ge, Si, etc. In FIG. 12,only the Co-Cr-Pt-based magnetic alloys are exemplified, but Mo, W, Si,and Ge hold valid in place of Cr. A preferable concentration of at leastone of these other elements of the group is 1 to 15 at. %.

FIG. 7 shows relationships between the Cr concentration and the inplanecoercivity Hc when Cr is added to Co-Pt as typical of the secondadditive element, and it is desirable to add at least 1 at. %,particularly 3 at. % or more of Cr to Co-Pt, because the inplanecoercivity exceeds 1,200 Oe thereby. Addition of more than 17 at. % ofCr is not desirable, because the saturation magnetization isdeteriorated. Thus, an effective concentration of the second element is1 to 17 at. %, except for Si, whose effective concentration is 1 to 40at. %.

The nonmagnetic metallic underlayer of magnetic recording media shown inFIGS. 6 and 7 is composed of Cr, and it is needless to say that similareffects can be obtained with other than Cr, i.e. Mo, W, V, Nb or Ta oralloys containing these metals as the main component.

The concentration of oxygen in the magnetic layer will be described inmore detail below.

When the present Co-based alloy containing the first and second additiveelements further contains 0.1 to 10 at. % of oxygen, not only thecomponent of inplane (1010) orientation (as will be hereinafter referredto "(100) orientation") of hexagonal closed packed (hcp) structure, butalso the component of perpendicular (0001) orientation (as will behereinafter referred to as "(001) orientation") is increased even on anonmagnetic metallic substrate of body-centered cubic (bcc) structure ofCr, Mo, W, etc. That is, from the crystallographic viewpoint, a ratio of002 X-ray diffraction peak intensity to 100 X-ray diffraction peakintensity of Co-based alloy becomes more than 3 as shown in FIG. 13A andFIG. 13B, and from the magnetic viewpoint, a perpendicular anisotropy isgiven in addition to the basic inplane anisotropy, and the c-axis ofCo-based alloy becomes substantially isotropic. As shown in FIG. 8, theinplace coercive squareness S* will be 0.85 or less, or further 0.8 orless with increasing thickness of the nonmagnetic metallic underlayer,because the second additive element such as Cr, Mo or W is liable tosegregate not only at the crystalline boundary but also in thecrystalline grains with the help of oxygen and/or the crystalline grainsare made finer and/or the crystalline grains component thatperpendicularly orient are increased. With an increase in theperpendicular anisotropy, the width of magnetic transition regionbecomes smaller, resulting in a decrease in the media noise. Thus, thisis preferable. The oxygen concentrations of the magnetic layers of thepresent invention shown in FIGS. 6 and 7 are 1 and 1.5 at. %,respectively.

The fourth object of the present invention can be attained by a magneticmemory apparatus, which comprises a magnetic recording medium, a drivingmeans for turning the magnetic recording medium, a magnetic head, a headaccess means, and a read and write means for the magnetic head, wherethe magnetic recording medium is composed of a magnetic recording mediumfor longitudinal recording, capable of attaining the first or secondobject or both objects of the present invention.

When the present magnetic recording media were subjected to read andwrite runs with a metal-in-gap (MIG) type or thin film head providedwith a ferromagnetic metal such as Co-Nb-Zr, Fe-Al-Si, Ni-Fe, etc. at aposition near the working gap, it was found that the read output wasremarkably increased at an inplane coercivity Hc of 1,200 Oe or more inthe circumferential direction of disk, as shown in FIG. 10. An inplanecoercivity of 1,500 or more is more preferable, because the recordingdensity can be further increased. When at least a portion of themagnetic pole is made of a ferromagnetic metal as mentioned above, therecording magnetic field can be intensified. Thus, use of aferromagnetic metal is quite suitable for a magnetic recording mediumwith a high coercivity as in the present invention and can improve theread and write characteristics, particularly in a magnetic memoryapparatus of larger capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a magnetic recording mediumaccording to one embodiment of the present invention.

FIG. 2 is a characteristic diagram of media noise of magnetic recordingmedia according to the present invention.

FIGS. 3 and 4 are characteristic diagrams of inplane coercivity ofmagnetic recording media according to the present invention.

FIG. 5 is a noise diagram of magnetic recording media according to thepresent invention.

FIG. 6 is a characteristic curve diagram showing relationships between aPt concentration of a magnetic layer and an inplane coercivity Hc ofmagnetic recording media according to the present invention.

FIG. 7 is a characteristic curve diagram showing relationships between aCr concentration of a magnetic layer and a inplane coercivity Hc ofmagnetic recording, media according to the present invention.

FIG. 8 is a characteristic curve diagram showing relationships betweenan underlayer thickness, and a coercive squareness and an inplanecoercivity of magnetic recording media according to the presentinvention.

FIG. 9 is a diagram showing relationship between a Pt concentration anda device S/N ratio of magnetic recording media according to the presentinvention.

FIG. 10 is a characteristic curve diagram showing relationships betweenan inplane coercivity and a read output of recording magnetic mediaaccording to the present invention.

FIG. 11 is a characteristic curve diagram showing relationships betweenan inplane coercive squareness S* and a media noise of magneticrecording media according to the present invention.

FIG. 12 is a characteristic curve diagram of corrosion resistance ofCo-Cr-Pt-based, quaternary magnetic alloy layer of magnetic recordingmedia according to the present invention.

FIGS. 13A and 13B are diagrams showing an X-ray diffraction pattern andcrystallographic orientation of magnetic recording media according tothe present invention.

FIGS. 14A and 14B are vertically cross-sectional and plan schematicviews of a magnetic memory apparatus according to the present invention,respectively.

FIG. 15 is a diagram showing magnetic properties of magnetic recordingmedia according to the present invention.

FIG. 16 is a diagram showing magnetic properties of magnetic recordingmedia according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1

One embodiment of the present invention will be described below,referring to FIG. 1, where numeral 10 is a substrate of strengthenedglass, plastics, Ni-P-plated Al alloy or the like; 11 and 11' aremetallic underlayers of pure metal of Cr, Mo or W, or an alloy of Cr-Ti,Cr-Si, Cr-Mo, Cr-W or the like; 12 and 12' are magnetic layers ofmagnetic alloy comprising Co, a material composed of at least oneelement selected from the group consisting of Cr, Mo and W, a materialcomposed of at least one element selected from the group consisting ofTi, Zr, Hf, Ta, Nb, Ru and Rh, and a material composed of at least oneelement selected from the group consisting of Al and Si; 13 and 13' arenonmagnetic protective layers composed of C, B, and S, or carbide,nitride, oxide or boride of Ti, Zr, Hf, Nb, Ta, V, Cr, Mo and W; and 14and 14' are lubricant layers composed of perfluoroalkylpolyether, or thelike.

The embodiment will be explained in detail below.

An Al-Mg alloy substrate, 89 mm in diameter, plated with Ni-P each to athickness of 12 μm, was treated with abrasive grains, 2 μm is size, togive fine scars approximately in the circumferential direction on thesubstrate surface. The thus treated substrate with a surface roughnessof 12 nm in the radial direction in terms of centerline averageroughness was used as the substrate 10 for a magnetic disk. Then, Crunderlayers 11 and 11' were at first formed on both sides of thesubstrate 10 each to a thickness of 400 nm, then magnetic layers 12 and12' of composition shown in Table 1 were formed on the Cr underlayerseach to a thickness of 60 nm and finally carbon protective layers 13 and13' are formed on the magnetic layers each to a thickness of 40 nm by DCmagnetron sputtering at a substrate temperature of 100° C. under an Argas pressure of 15 mTorr with an input power density of 2 W/cm². Then,liquid lubricant layers 14 and 14' of perfluoroalkylpolyether wereformed on the carbon protective layers each to a thickness of 6 nm tomake a magnetic disk.

                  TABLE 1                                                         ______________________________________                                                                 Media                                                         Magnetic layer  noise                                                ______________________________________                                        Composition                                                                   No.                                                                           1          (Co.sub.0.9 Cr.sub.0.1).sub.0.9 Ti.sub.0.05 Si.sub.0.05                                         5.6 μVrms                                     2          (Co.sub.0.9 Cr.sub.0.1).sub.0.9 Zr.sub.0.05 Si.sub.0.05                                         5.5 μVrms                                     3          (Co.sub.0.9 Cr.sub.0.1).sub.0.9 Hf.sub.0.05 Si.sub.0.05                                         5.4 μVrms                                     4          (Co.sub.0.9 Cr.sub.0.1).sub.0.9 Ta.sub.0.05 Si.sub.0.05                                         5.3 μVrms                                     5          (Co.sub.0.9 Cr.sub.0.1).sub.0.9 Nb.sub.0.05 Si.sub.0.05                                         5.2 μVrms                                     6          (Co.sub.0.9 Cr.sub.0.1).sub.0.93 Ru.sub.0.02 Si.sub.0.05                                        5.7 μVrms                                     7          (Co.sub.0.9 Cr.sub.0.1).sub.0.93 Ru.sub.0.02 Si.sub.0.05                                        5.7 μVrms                                     8          (Co.sub.0.87 Cr.sub.0.13).sub.0.91 Ti.sub.0.05 Al.sub.0.04                                      5.5 μVrms                                     9          (Co.sub.0.87 Cr.sub.0.13).sub.0.91 Zr.sub.0.05 Al.sub.0.04                                      5.4 μVrms                                     10         (Co.sub.0.87 Cr.sub.0.13).sub.0.91 Hf.sub.0.05 Al.sub.0.04                                      5.3 μVrms                                     11         (Co.sub.0.87 Cr.sub.0.13).sub.0.91 Ta.sub.0.05 Al.sub.0.04                                      5.1 μVrms                                     12         (Co.sub.0.87 Cr.sub.0.13).sub.0.91 Nb.sub.0.05 Al.sub.0.04                                      5.0 μVrms                                     13         (Co.sub.0.87 Cr.sub.0.13).sub.0.93 Ru.sub.0.02 Al.sub.0.04                                      5.6 μVrms                                     14         (Co.sub.0.87 Cr.sub.0.13).sub.0.93 Rh.sub.0.02 Al.sub.0.04                                      5.7 μVrms                                     Comparative                                                                              (Co.sub.0.9 Cr.sub.0.1).sub.0.96 Ta.sub.0.04                                                    8.5 μVrms                                     ______________________________________                                    

The read and write characteristics of the thus obtained disks wereevaluated as media noise at 7 MHz recording with a metal-in-gap (MIG)head having a gap length of 0.6 μm (Fe-Al-Si alloy used at the head tipend) at a head-to-media velocity of 15 m/sec. The media noise was foundto be lower in all the compositions than that of comparative compositionand thus a higher S/N ratio was obtained. The magnetic disks were placedin a magnetic disk apparatus to evaluate the corrosion resistance. Evenif the apparatus was left standing in a high temperature/humidityatmosphere at 65° C. and 85% RH for 3 months, no generation of read andwrite error was observed at all in read and write tests at a highdensity of 50 Mb/in², which is a higher areal density than that on theconventional media. That is, a distinguished corrosion resistance wasobtained.

Another embodiment of the present invention in the same structure asshown in FIG. 1 will be explained below.

On both sides of a strengthened glass substrate, 51 mm in diameter,whose surfaces were roughened to form fine irreguralities approximatelyin the circumferential direction by chemical or physical etching orboth, making a surface roughness of 10 nm in the radial direction interms of centerline average roughness were formed Cr underlayers each toa thickness of 300 nm, magnetic layers of (Co₀.88 Cr₀.12)₀.90 Ta₀.03Si₀.07 each to a thickness of 50 nm and ZrN protective layers each to athickness of 25 nm in succession by sputtering at a substratetemperature of 150° C. in an Ar gas containing 0.05 to 0.5 vol. % ofoxygen under an Ar gas pressure of 10 mTorr with an input power densityof 5 W/cm². Finally, layers of perfluoroalkylpolyether-based lubricantcontaining end groups having an anchoring capacity were formed thereoneach to a thickness of 4 nm to make a magnetic disk.

Analysis of oxygen concentration in the magnetic layers by Augerelectron spectroscopy revealed that the magnetic layers contained 1 at.% to 8 at. % of oxygen. The thus obtained magnetic disks were subjectedto read and write tests at a head-to-media velocity of 10 m/s and 5 MHzwith the same magnetic head as used above and especially lower medianoises of less than 4.5 μVrms were observed in all of the magneticdisks, and were found to be better than those when no oxygen wascontained in the magnetic layers (5 μVrms). As to the corrosionresistance, a better result was obtained than that when no oxygen wascontained in the magnetic layers. Similar results were also obtained inmagnetic recording media with metallic underlayers of pure metal of Moor W, or an alloy of Cr-Ti, Cr-Si or Cr-Mo.

With a thin film head or a metal-in-gap (MIG) head and 1 to 4 plattersof the thus obtained magnetic disks, 89 mm in diameter or 51 mm indiameter, magnetic disk apparatuses of large capacity such as a higherrecording density of 50 Mb/in² to 70 Mb/in² in terms of areal recordingdensity than that of the conventional media could be made. When theCapacity was the same as the conventional, the number of magnetic diskscould be reduced or the size of the magnetic disks could be madesmaller, so that the apparatus could be made smaller in size by at least30%. At least two-fold corrosion resistance could be obtained in any ofthe present apparatuses, as compared with an apparatus using theconventional metallic longitudinal recording media. That is, the presentmagnetic disk apparatuses had remarkably distinguished capacity,reliability, etc., as compared with conventional magnetic diskapparatuses.

In the foregoing, magnetic disk apparatus have been explained, but thepresent invention is not limited thereto, but is also applicable to suchmagnetic recording application apparatuses such as magnetic tapeapparatuses, magnetic floppy disk apparatuses, magnetic cardapparatuses, magnetic image apparatuses, magnetic drum apparatuses, etc.

As explained above, the present invention can provide magnetic recordingmedia with a high corrosion resistance, a smaller media noise and ahigher S/N ratio at read and write runs particularly at a high recordingdensity than those of the conventional metallic longitudinal recordingmedia, and thus is particularly effective for a smaller size, a largecapacity and a higher reliability of a magnetic memory apparatuses.

Example 2

Further embodiment of the present invention will be explained below,referring also to FIG. 1, where numeral 10 is a substrate ofstrengthened glass, plastics, Ni-P-plated Al alloy or the like; 11 and11' are nonmagnetic metallic underlayers of pure metal of Cr, Mo or W oralloy of Cr-Ti, Cr-Si, Cr-Mo, Cr-W or the like; 12 and 12' are magneticlayers of a magnetic alloy comprising Co and Pt, a material composed ofat least one element selected from the group consisting of Ni, Cr, Moand W, a material composed of at least one element selected from thegroup consisting of Ti, Zr, Hf, Ta, Nb, Ru and Rh, and a materialcomposed of at least one element selected from the group consisting ofAl and Si; 13 and 13' are nonmagnetic protective layers composed of C, Bor Si or carbide, nitride, oxide or boride of Ti, Zr, Hf, Nb, Ta, V, Cr,Mo or W; and 14 and 14' are lubricating layers ofperfluoroalkylpolyether or the like.

The embodiment will be explained in more detail below.

An Al-Mg alloy substrate, 130 nm in diameter, plated with Ni-P on bothsides each to a thickness of 10 nm was treated with abrasive grains, 1μm in size, to provide fine scan approximately in the circumferentialdirection on the surfaces, and thus the magnetic disk substrate having asurface roughness of 10 nm in the radial direction in terms ofcenterline average roughness was obtained.

On both surfaces of the substrate were formed Cr layers each to athickness of 500 nm, then magnetic layers of magnetic alloy compositionshown in Table 2 each to a thickness of 50 nm and a then C protectivelayers each to a thickness of 30 nm in succession by DC magnetronsputtering at a substrate temperature of 120° C. under an Ar gaspressure of 10 mTorr with an input power density of 1 W/cm². Finally,layers of perfluoroalkylpolyether-based liquid lubricant were formedthereon each to a thickness of 4 nm to make a magnetic disk.

                  TABLE 2                                                         ______________________________________                                                                    Media                                             Magnetic layer             noise N.sub.P                                      ______________________________________                                        Composi-                                                                      tion                                                                          No.                                                                           1       (Co.sub.0.7 Ni.sub.0.3).sub.0.85 Ti.sub.0.05 Si.sub.0.05 Pt.sub.0.            05                     4.4 μVrms                                   2       (Co.sub.0.7 Ni.sub.0.3).sub.0.85 Zr.sub.0.05 Si.sub.0.05 Pt.sub.0.            05                     4.3 μVrms                                   3       (Co.sub.0.7 Ni.sub.0.3).sub.0.85 Hf.sub.0.05 Si.sub.0.05 Pt.sub.0.            05                     4.2 μVrms                                   4       (Co.sub.0.7 Ni.sub.0.3).sub.0.85 Ta.sub.0.05 Si.sub.0.05 Pt.sub.0.            05                     4.6 μVrms                                   5       (Co.sub.0.7 Ni.sub.0.3).sub.0.85 Nb.sub.0.05 Si.sub.0.05 Pt.sub.0.            05                     4.7 μVrms                                   6       (Co.sub.0.7 Ni.sub.0.3).sub.0.85 Ru.sub.0.05 Si.sub.0.05 Pt.sub.0.            05                     4.9 μVrms                                   7       (Co.sub.0.7 Ni.sub.0.3).sub.0.85 Rh.sub.0.05 Si.sub.0.05 Pt.sub.0.            05                     5.0 μVrms                                   8       (Co.sub.0.88 Cr.sub.0.12).sub.0.85 Ti.sub.0.05 Si.sub.0.05                    Pt.sub.0.05            4.5 μVrms                                   9       (Co.sub.0.88 Ni.sub.0.12).sub.0.85 Zr.sub.0.05 Al.sub.0.05                    Pt.sub.0.05            4.3 μVrms                                   10      (Co.sub.0.88 Cr.sub.0.12).sub.0.85 Hf.sub.0.05 Al.sub.0.05                    Pt.sub.0.05            4.4 μVrms                                   11      (Co.sub.0.88 Cr.sub.0.12).sub.0.85 Ta.sub.0.05 Al.sub.0.05                    Pt.sub.0.05            4.2 μVrms                                   12      (Co.sub.0.88 Cr.sub.0.12).sub.0.85 Nb.sub.0.05 Al.sub.0.05                    Pt.sub.0.05            4.3 μVrms                                   13      (Co.sub.0.88 Cr.sub.0.12).sub.0.85 Ru.sub.0.05 Al.sub.0.05                    Pt.sub.0.05            4.9 μVrms                                   14      (Co.sub.0.88 Cr.sub.0.12).sub.0.85 Rh.sub.0.05 Al.sub.0.05                    Pt.sub.0.05            4.0 μVrms                                   15      (Co.sub.0.88 M.sub.0.12).sub.0.85 Ta.sub.0.05 Si.sub.0.05                     Pt.sub.0.05            4.0 μVrms                                   16      (Co.sub.0.88 W.sub.0.12).sub.0.85 Ta.sub.0.05 Si.sub.0.05                     Pt.sub.0.05            4.5 μVrms                                   17      (Co.sub.0.65 Ni.sub.0.30 Cr.sub.0.05).sub.0.85 Zr.sub.0.05                    Si.sub.0.05 Pt.sub.0.05                                                                              4.0 μVrms                                   18      (Co.sub.0.65 Ni.sub.0.30 Mo.sub.0.05).sub.0.85 Zr.sub.0.05                    Si.sub.0.05 Pt.sub.0.05                                                                              4.1 μVrms                                   19      (Co.sub.0.65 Ni.sub.0.30 W.sub.0.05).sub.0.85 Zr.sub.0.05                     Si.sub.0.05 Pt.sub.0.05                                                                              4.2 μVrms                                   20      (Co.sub.0.80 Ni.sub.0.10 Cr.sub.0.10).sub.0.85 Ta.sub.0.05                    Si.sub.0.05 Pt.sub.0.05                                                                              4.0 μVrms                                   Compar- (Co.sub.0.7 Ni.sub.0.3).sub.0.95 Zr.sub.0.05                                                         7.0 μVrms                                   ative                                                                         ______________________________________                                    

The read and write characteristics of the thus obtained magnetic diskswere evaluated as media noise at 9 MHz recording with a Mn-Zn ferritering head having a gap length of 0.7 μm at a head-to-media velocity of20 m/s. The media noise was found to be not more than 5 μVrms in all thecompositions, which were smaller than the head noise, amplifier noise orComparative Case, and thus a higher S/N ratio was obtained, as comparedwith that of the conventional media. In a high temperature/humiditycorrosion test of all of the media at 60° C. and 80% RH, no generationof read and write error was observed even after two weeks of the test,and a good corrosion resistance was obtained.

Example 3

Still further embodiment of the present invention in the same structureas shown in FIG. 1 will be explained below

On both sides of a strengthened glass substrate, 89 mm in diameter,whose surfaces were roughened to form fine irregularities approximatelyin the circumferential direction by chemical or physical etching orboth, making a surface roughness of 15 nm in the radial direction interms of centerline agerage roughness, were formed Cr underlayers eachto a thickness of 350 nm, magnetic layers of (Co₀.6 Ni₀ .4)₀.88 Zr₀.04Al₀.04 Pt₀.04 each to a thickness of 60 nm and protective layers of ZrO₂each to a thickness 30 nm at a substrate temperature of 100° C. in an Argas containing 0.1 vol. % to 0.7 vol. % of oxygen under an Ar gaspressure of 15 mTorr with an input power density of 2 W/cm². Then,layers of perfluoroalkylpolyether-based lubricant containing end grouphaving an anchoring capacity were formed thereon each to a thickness of5 nm to make a magnetic disk.

Analysis of oxygen concentration in the magnetic layers by Augerelectron spectroscopy revealed that the magnetic layers contained 2 at.% to 10 at. % of oxygen. The thus obtained magnetic disks were subjectedto read and write tests at a head-to-media velocity of 15 m/s and 7 MHzwith the same magnetic head as used in Example 2 and especially lowermedia noises of less than 4 μVrms were observed in all of the magneticdisks and were found to be better than those when no oxygen wascontained in the magnetic layers (4.5 Vrms). As to the corrosionresistance, a better result was obtained than that when no oxygen wascontained in the magnetic layers.

Similar results were also obtained in magnetic recording media withmetallic underlayers of pure metal of Mo or W, or an alloy of Cr-Si orCr-Ti.

With a thin film head or metal-in-gap (MIG) head and 4 to 8 platters ofthe thus obtained magnetic disks, 89 mm in diameter or 130 mm indiameter, magnetic disk apparatuses of large memory capacity such as anareal recording density of 60 Mb/in² or more and an apparatus capacityof 200 MB or more were made. As compared with the apparatuses using theconventional metallic thin film media, approximately 2-fold corrosionresistance and better antiwear reliability were obtained and also thememory capacity, reliability, etc. were considerably improved.

When the present magnetic recording media were applied to magnetic diskapparatuses of equivalent areal recording density to the conventionalone, the head-to-media spacing could be made lower than the conventionalone and thus the antiwear reliability could be made higher at leasttwice. When the present magnetic recording media were used at ahead-to-media spacing equal to or less than the conventional one, theareal recording density could be made higher at least twice, and thusthe magnetic disk apparatuses could be made smaller in size and largerin capacity.

In the foregoing, explanation has been made mainly of magnetic diskapparatuses. The present invention is also applicable to any ofapparatuses based on magnetic recording such as magnetic cardapparatuses, magnetic image apparatuses, magnetic tape apparatuses,floppy disk apparatuses, magnetic drum apparatuses.

As explained above, the present invention provides magnetic recordingmedia and magnetic memory apparatuses with a reduced media noise levelat read and write runs at a high recording density by at least 1.5-fold,as compared with the conventional apparatuses and capable of reading andwriting information of high density in a high S/N ratio and also with agood corrosion resistance of madia and hi9her performance andreliability. Thus, the present invention is effective for higherrecording density and higher reliability particularly of magnetic memoryapparatuses.

Example 4

In FIG. 1 showing a cross-sectional view of a magnetic recording mediumaccording to the present invention, numeral 11 is a nonmagneticsubstrate of nonmagnetic Al alloy plated with Ni-P, Ni-P-W, or the like,or chemically strengthened glass or the like; 12 and 12' are nonmagneticmetallic underlayers of pure metal of body centered cubic (bcc)structure composed of at least one element selected from the groupconsisting of Cr, Mo, W, V, Nb and Ta, or an alloy containing theseelements as main components, or the pure metal or alloy furthercontaining at least one element selected from the group consisting ofTi, Si, Ge, Cu, Pt, Rh, Ru, Re, Pd and oxygen, formed on both sides ofthe substrate; 13 and 13' are magnetic layers of Co-based alloycomprising 1 to 35 at. % of at least one first additive element selectedfrom the group consisting of Pt and Ir, 1 to 17 at. % of at least onesecond additive element selected from the group consisting of Ti, Zr,Hf, V, Nb, Ta, Cr, Mo, V, Ge and Si, except for Si, whose concentrationis 1 to 40 at. %, and 0.1 to 10 at. % of oxygen, the balance being Co,formed on the underlayers, respectively; and 14 and 14' are protectivelayers comprising C, B, B₄ C, Si-C, Co₃ O₄, SiO₂, Si₃ N₄, W-C, Zr-W-C,Zr-Nb-N, or the like, formed on the magnetic layers, respectively, andthe foregoing magnetic recording medium was made in the followingmanner.

An aluminum alloy disk substrate containing 4 wt. % of magnesium, 130 mmin outer diameter, 40 mm in inner diameter and 1.9 mm in thickness, wasplated with Ni-12 wt. % P each to a thickness of 20 μm on both sides ofthe substrate and further polished each to a thickness of 15 μm on bothsides to have fine irregularities in the circumferential direction(head-moving direction) to make a centerline average roughness of 10 nm.The surface treatment (polishing) is usually called "texturingtreatment". Then, the substrate was washed and then nonmagnetic metallicunderlayers, magnetic layers and protective layers were formed insuccession on both sides of the substrate by initial evacuation to2×10⁻⁶ Torr and then by RF magnetron sputtering in a discharge Ar gasatmoshere containing 0.2 vol. % of oxygen under an Ar gas pressure of 15mTorr at a substrate temperature of 110° C. with an input power densityof 1.6 W/cm² to make a magnetic recording medium for longitudinalrecording. The nonmagnetic metallic layers were Cr layers containing 4at. % of oxygen, the magnetic layers were composed of Co-15 at. % Cr-11at. Pt alloy (containing 3 at. % of oxygen), and the protective layerswere made of carbon. On the protective layers, lubricant layers ofperfluoroalkylpolyether, or the like can be provided. When the thicknessof Co-15 at. % Cr-11 at. % Pt was changed from 10 to 90 nm while keepingthe thickness of Cr underlayers as the nonmagnetic metallic underlayersconstant to 500 nm, static magnetic properties as shown in Table 3 wereobtained.

                  TABLE 3                                                         ______________________________________                                        Static magnetic properties                                                    of C/Co--Cr--Pt/Cr layers                                                                     Inplane   Coercive                                            Thickness of    coercivity                                                                              squareness                                          Co--Cr--Pt layer                                                                              (Hc)      (S*)                                                ______________________________________                                        10 nm           1560 Oe   0.385                                               20 nm           2250 Oe   0.738                                                                (760)    (0.86)                                              30 nm           2415 Oe   0.776                                                               (1120)    (0.88)                                              45 nm           1925 Oe   0.769                                                               (1055)    (0.91)                                              60 nm           1820 Oe   0.742                                                               (1070)    (0.92)                                              75 nm           2005 Oe   0.789                                                                (960)    (0.92)                                              90 nm           1950 Oe   0.826                                                                (900)    (0.92)                                              ______________________________________                                    

In Table 3, numerical values in the parentheses show comparative valueswhen no nonmagnetic metallic under-layers were provided. As is apparentfrom the comparative values, the presence of the nonmagnetic metallicunderlayers play an important role in the improvement of magneticproperties, and such distinguished properties were obtained as aninplane coercivity Hc of more than 1,500 Oe while fully satisfying thecondition of coercive squareness S*≦0.85.

Even if the thickness of Cr layers as the nonmagnetic metallicunderlayers was changed to 50, 100, 200, 300 and 400 nm, the coercivesquareness S* was increased with increasing thickness of the magneticlayers, and was in a more preferable range of 0.85≧S* ≧0.6, so long asthe thickness of the magnetic layers was 15 nm or more. The coercivesquareness S* is an average of values in the circumferential directionof disk, that is, the head moving direction and values in the radialdirection, and the inplane coercivity Hc is a value in thecircumferential direction of disk (these definitions will be applied toExamples and Comparative Examples which follow). Similar results wereobtained with a surface roughened strengthened glass and analumite-treated alloy disk substrate by a chemical etching treatment inplace of NiP-plated Al alloy substrate.

Comparative Example 1

A magnetic recording medium was prepared in the same manner as inExample 4 except that the alloy composition of the magnetic layers waschanged to Co-20 at. % Ni-15 at. % Pt and the thickness of the magneticlayers was also changed to 90 nm, and it was found that the inplanecoercivity Hc was 860 Oe. In spite of the presence of Cr layers as thesame nonmagnetic metallic underlayers as in Example 4, the inplanecoercivity Hc was largely lowered owing to a difference in the alloycomposition of the magnetic layers. That is, Comparative Example 1 is acase where no second additive element of the present invention wascontained.

Example 5

Magnetic recording media were prepared in the same manner as in Example4 except that a load-lock type DC magnetron sputtering apparatus wasused as an apparatus for forming a magnetic recording medium forlongitudinal recording, and Cr underlayers having a thickness of 400 nmand magnetic layers of composition shown in Table 5 having a thicknessof 50 nm were formed in successive by initial evacuation to 1×10⁻⁶ Torrand then by DC magnetron sputtering in a discharge A gas atmospherecontaining 0.1 vol. % of oxygen under an Ar gas pressure of 10 mTorr ata substrate temperature of 150° C. with an input power density of 1.6 to4.8 W/cm², and then protective layers were formed thereon under adischarge gas pressure of 3 mTorr. All of the magnetic layers and Crunderlayers contained 1 at. % of oxygen.

                  TABLE 5                                                         ______________________________________                                        Composition of magnetic layers                                                Comp. No.  Magnetic layers                                                    ______________________________________                                        201        Co-15 at. % Cr-11 at. % Pt-1 at. % Si                              202        Co-15 at. % Cr-3 at. % Ti-8 at. % Pt                               203        Co-15 at. % Cr-3 at. % Zr-8 at. % Pt                               204        Co-15 at. % Cr-3 at. % Hf-8 at. % Pt                               205        Co 15 at. % Cr-3 at. % Ta-8 at. % Pt                               206        Co-15 at. % Cr-3 at. % Nb-8 at. % Pt                               207        Co-13 at. % Mo-13 at. % Pt                                         208        Co-13 at. % W-13 at. % Pt                                          209        Co-13 at. % V-13 at. % Pt                                          210        Co-20 at. % Si-2 at. % Ta-10 at. % Pt                              211        Co-10 at. % Ge-2 at. % Ta-10 at. % Pt                              212        Co-20 at. % Si-2 at. % Zr-10 at. % Pt                              213        Co-10 at. % Ge-2 at. % Zr-10 at. % Pt                              214        Co-20 at. % Si-2 at. % Nb-10 at. % Pt                              215        Co-20 at. % Ge-2 at. % Nb-10 at. % Pt                              216        Co-13 at. % Ti-13 at. % Pt                                         217        Co-13 at. % Zr-13 at. % Pt                                         218        Co-13 at. % Hf-13 at. % Pt                                         219        Co-13 at. % Nb-13 at. % Pt                                         220        Co-13 at. % Ta-13 at. % Pt                                         221        Co-10 at. % Mo-6 at. % Ti-10 at. % Pt                              222        Co-10 at. % Cr-2.7 at. % Mo-10 at. % Pt                            223        Co-17 at. % Cr-4 at. % Mo-5 at. % Ir                               224        Co-13 at. % Cr-4 at. % Mo-20 at. % Pt                              225        Co-3 at. % Cr-20 at. % Pt                                          226        Co-13 at. % Cr-12 at. % Pt-1 at. % Ir                              ______________________________________                                    

It was found that all of the magnetic recording media had an inplanecoercivity of 1,400 Oe or more. Particularly when the inplane coercivitywas 1,500 Oe or more, the linear recording density at -3 dB signalvalues was 35 kFCI or more irrespective of the compositions of themagnetic layers, and the signal-to-noise ratio (S/N) of these recordingmedia was by about 20% higher than the S/N of the conventional media.However, even in the recording media with magnetic layers of alloycompositions formed in a discharge Ar gas atmosphere containing 0.1 vol.% of oxygen, which had an inplane coercivity of 1,500 Oe or more, theinplane coercivity was decreased to 1,200 Oe or less and a S/N ratio waslower, when the leak rate was large or the Ar gas atmosphere containednitrogen, etc.

These media were subjected to NaCl spray test with a salt solutioncontaining 0.001 mol/l of NaNO₃ and 0.1 Mol/l of NaCl to evaluate thecorrosion resistance, and it was found that those having magnetic layerscontaining at least one element of Ti, Zr, Hf, Ta and Nb as the secondadditive element had a corrosion resistance at least twice as high asthat of those having magnetic layers based on the other alloys.Particularly, in case of quaternary alloys shown in Compositions Nos.201 to 206, 210 to 215, 221 and 223, highest linear recording density at-3dB signal values, such as 40 kFCI or more were obtained together withparticularly better overwrite characteristics and corrosion resistance.

These media were etched using an acid solution containing 0.6 N of HCland 0.07 N of HNO₃, and the segregation structure was examined by TEMand SEM. The quaternary alloy disks with highest linear recordingdensity had more remarkable segregation structure in the magnetic grainsthan ternary alloy disks.

Similar results were obtained with nonmagnetic metallic underlayers ofpure metal of Mo, W, V, Nb, or Ta, or an alloy of Cr-Ti, Cr-W, Cr-Mo,Cr-Si, Cr-Pt, Mo-Ti, W-V, V-Si, Nb-Cr, or Ta-Cr. Particularly in case ofunderlayers of Cr-20 at. % Ti, Cr-20 at. % Si, Cr-1 at. % Pt and Mo-20at. % Ti, highest S/N ratios were obtained. In any of these underlayers,there were no intermtallic compounds between Co and the elements ofunderlayer components.

Example 6

An aluminum alloy disk substrate containing 4 wt. % of magnesium, 130 mmin outer diameter, 40 nm in inner diameter and 1.9 mm in thickness, wasplated with Ni-12 wt. % P each to a thickness of 20 μm on both sides ofthe substrate. Then, the substrate was polished each to a thickness of15 μ to give fine irregularities in the circumferential direction sothat the centerline average roughness can be 5 nm. Then, the substratewas washed and nonmagnetic metallic underlayers, magnetic layers andprotective layers were formed in succession on both sides of thesubstrate by initial evaculation to 2×10⁻⁶ Torr and by RF magnetronsputtering in a discharge Ar gas atmosphere containing 0.5 vol. % ofoxygen under a discharge Ar gas pressure of 15 mTorr at a substratetemperature of 100° C. with an input power density of 1.6 W/cm² to makea magnetic recording medium for longitudinal recording. The nonmagneticmetallic underlayers were composed of Cr, the magnetic layers werecomposed of an alloy of Co-8 at.Cr-3 at. % Ta-13 at. % Pt containing 6at. % of oxygen, and the protective layers were composed of carbon.Lubricant layers of perfluoroalkylether can be provided on theprotective layers.

When the thickness of the magnetic layers of Co-8 at. % Cr-3 at. % Ta-13at. % Pt alloy containing 6 at. % of oxygen was changed from 10 to 90 nmwhile keeping the thickness of Cr layers as the nonmagnetic metallicunderlayers constant to 500 nm, static magnetic properties as shown inTable 6 were obtained. Similar results were obtained when the thicknessof Cr layers was changed to 100, 150, 200, 300, 400, 600 and 700 nm.However, when the thickness of Cr layers was 100 nm, the number ofpin-on-disk test runs for the antiwear strength was less than 5,000,which was less than one-fourth of the strength in case of the thicknessof Cr layers of 150 nm or more and thus the antiwear strength was verypoor. When the thickness of Cr layers was 700 nm, the head-to-mediaspacing was not made less than 25 μm at the magnetic disk driving. Onthe other hand, when the thickness of Cr layers was 600 nm or less, thehead-to-media spacing could be made as small as 0.1 μm and thereliability was considerably improved. Thus, a practically preferablethickness of Cr layers is 150 to 600 nm.

                  TABLE 6                                                         ______________________________________                                        Static magnetic properties                                                    of C/Co--Cr--Ta--Pt/Cr layers                                                                 Inplane   Coercive                                            Thickness of    coercivity                                                                              squareness                                          Co--Cr--Pt layer                                                                              (Hc)      (S*)                                                ______________________________________                                        10 nm           1540 Oe   0.510                                               20 nm           2105 Oe   0.752                                               30 nm           2370 Oe   0.784                                               45 nm           1855 Oe   0.778                                               60 nm           1870 Oe   0.802                                               75 nm           1950 Oe   0.765                                               90 nm           1905 Oe   0.782                                               ______________________________________                                    

Example 7

Cr magnetic metallic underlayers having a thickness of 400 nm andmagnetic layers of composition shown in Table 7 which had a thickness of50 nm were formed in succession on the same substrate as used in Example6 by initial evacuation to 1×10⁻⁶ Torr and by load-lock type, DCmagnetron sputtering in a discharge Ar gas atmosphere containing 0.05vol. % of oxygen under an Ar gas pressure of 10 mTorr at a substratetemperature of of 200° C. with an input power density of 1.6 to 4.8W/cm² and then protective layers were formed under a discharge Ar gaspressure of 3 mTorr, where other conditions were the same as in Example6.

All of the thus prepared magnetic recording media had an inplanecoercivity of 1,500 Oe or more, the media having an inplane coercivityof 1,500 Oe or more had a linear recording density at -3 dB signalvalues of 35 kFCl or more, and the noise ratio (S/N) of these media wasby about 20% higher than the S/N ratio of the conventional media havingmagnetic layers of Co-Ni alloy. Particularly, the magnetic disks ofcompositions Nos. 417 to 421 had particularly better overwritecharacteristics and the leakage recording efficiency and eraseefficiency in the track width direction were highest and the broadestmargin for the position error was obtained. The magnetic disks ofcomposition Nos. 417 to 421, 401 and 415 had more remarkable segregationstructure at the magnetic grain boundaries and in the magnetic grains.

Then, the media were subjected to a NaCl spray test with a salt solutioncontaining 0.001 mol/l of NaCO₃ and 0. 1 mol/l of NaCl to evaluates thecorrosion resistance. It was found that the media having magnetic layerscontaining Ti, Zr, Hf, Ta, V or Nb as the second additive element had anat least two-fold corrosion resistance, as compared with the mediahaving magnetic layers containing Cr, Mo, W, Ce, Si, or the like. Thesame effect was obtained with nonmagnetic metallic underlayers of puremetal of Mo, W, V, Nb, or Ta, or an alloy of Cr-Ti,k Cr-W, Cr-Mo, Mo-Ti,W-V, V-Si, Nb-Cr or Ta-Cr. The magnetic layers and the nonmagneticmetallic underlayers contained 0.5 at. % of oxygen.

                  TABLE 7                                                         ______________________________________                                        Composition of magnetic layers                                                Comp. No.   Magnetic layers                                                   ______________________________________                                        401         Co-10 at. % Cr-15 at. % Pt                                        402         Co-3 at. % Cr-15 at. % Ir                                         403         Co-3 at. % Cr-3 at. % Ti-16 at. % Pt                              404         Co-3 at. % Cr-3 at. % Zr-16 at. % Pt                              405         Co-3 at. % Cr-3 at. %. Hf-16 at. % Pt                             406         Co-3 at. % Cr-3 at. % Ta-16 at. % Pt                              407         Co-3 at. % Cr-3 at. % Nb-16 at. % Pt                              408         Co-3 at. % Mo-22 at. % Pt                                         409         Co-5 at. % W-16 at. % Pt                                          410         Co-5 at. % V-16 at. % Pt                                          411         Co-5 at. % Mo-3 at. % Ti-16 at. % Pt                              412         Co-6 at. % Cr-2 at. % Mo-16 at. % Pt                              413         Co-5 at. % Cr-1.4 at. % Mo-16 at. % Pt                            414         Co-3 at. % Cr-1 at. % Ir-14 at. % Pt                              415         Co-10 at. % Cr-14 at. % Pt-1 at. % Ir                             416         Co-3 at. % Cr-22 at. % Pt                                         417         Co-10 at. % Cr-8 at. % Pt                                         418         Co-10 at. % Mo-8 at. % Pt                                         419         Co-10 at. % W-8 at. % Pt                                          420         Co-15 at. % Si-8 at. % Pt                                         421         Co-10 at. % Ge-8 at. % Pt                                         ______________________________________                                    

Example 8

Cr-20 at. % Ti metallic underlayers having a thickness of 400 nm andmagnetic layers of composition shown in Table 8, which had a thicknessof 50 nm were formed on the same substrate as used in Example 6 byinitial evacuation to 1×10⁻⁶ Torr and load-lock type, DC magneticsputtering in a discharge Ar gas atmosphere containing 0.05 vol. % ofoxygen under a discharge Ar gas pressure of 10 mTorr at a substratetemperature of 250° C. and the protective layers were formed under adischarge Ar gas pressure of 3 mTorr, where other conditions were thesame as in Example 6.

All of the thus obtained magnetic recording media had an inplancecoercity of 1,200 Oe or more. Particularly when the inplane coercivityof the media was 1,200 Oe or more, the linear recording density at -3 dBsignal values was 33 kFCl or more and the noise ratio (S/N) of thesemedia was about 15% higher than the S/N ratio of the conventional mediahaving magnetic layers of Co-Ni Alloy or Co-Cr alloy. The magneticlayers and the nonmagnetic metallic underlayers contained 0.2 at. % ofoxygen. The magnetic layers had a segregation structure at the gainboundaries and in the grains.

                  TABLE 8                                                         ______________________________________                                        Composition of magnetic layers                                                Comp. No.      Magnetic layers                                                ______________________________________                                        501            Co-10 at. % Cr-2.5 at. % Pt                                    502            Co-12 at. % Cr-2.5 at. % Pt                                    503            Co-14 at. % Cr-2.5 at. % Pt                                    504            Co-16 at. % Cr-2.5 at. % Pt                                    505            Co-9 at. % Cr-1.5 at. % Pt                                     506            Co-11 at. % Cr-1.5 at. % Pt                                    507            Co-13 at. % Cr-1.5 at. % Pt                                    508            Co-15 at. % Cr-1.5 at. % Pt                                    509            Co-15 at. % Si-2.5 at. % Pt                                    510            Co-10 at. % Ge-2.5 at. % Pt                                    ______________________________________                                    

Example 9

With 1 to 9 platters of magnetic recording media prepared in Examples 4to 8 and a metal-in-gap (MIG) type or thin film type magnetic headsusing Fe-Al-Si-Ru film having a thickness of 2 μm or Co-Nb-Zr filmhaving a thickness of 20 μm as magnetic pole tips, magnetic diskapparatuses were made. The resulting magnetic disk apparatuses had alarger capacity, for example, by at least 1.5-fold, than the capacity ofmagnetic disk apparatuses using the conventional coating media orlongitudinal media of Co-Ni alloy, and also had a higher reliability inthe antiwear properties, the corrosion resistance, etc. by at least2-fold.

Example 10

In a conventional magnetic memory apparatus comprising a magneticrecording medium, a driving means for turning the magnetic recordingmedium, a magnetic head, a head access means, and a read and write meansfor the magnetic head, any one of the magnetic recording medium shown inExamples 4 to 8 was used as the magnetic recording medium and a thinfilm type magnetic head whose magnetic pole was composed of Ni-Fe orCo-Ta-Zr was used.

The present invention can provide magnetic recording media capable ofreading and writing information at a high recording density and havingdisting reliabilities in the corrosion resistance, flyability andantiwear properties and also a magnetic memory apparatus of highcapacity.

What is claimed is:
 1. A magnetic recording medium for longitudinalrecording which comprises a nonmagnetic substrate, a nonmagneticmetallic underlayer composing at least one metal element selected fromthe group consisting of Cr, Mo, W, V, Nb and Ta, and containing 0.1 to10 at. % oxygen, formed on the nonmagnetic substrate, and a magneticlayer of Co-based alloy, formed on the nonmagnetic metallic underlayer,the magnetic layer comprising 1 to 35 at. % of at least one firstadditive element selected from the group consisting of Pt and Ir, 1 to17 at. % of at least one second additive element selected from the groupconsisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ge and Si, except forSi, whose concentration is 1 to 40 at. %, and 0.1 to 10 at. % of oxygen,sum total of the first and second additive elements and the oxygen being2.2 to 50 at. %.
 2. A magnetic recording medium for longitudinalrecording according to claim 1, wherein the second additive elementcomprises at least one element selected from the group A consisting ofCr, Mo, W, Ge and Si and at least one element selected from the group Bconsisting of Ti, Zr, Hf, V, Nb and Ta.
 3. A magnetic recording mediumfor longitudinal recording according to claim 1, wherein the secondadditive element comprises at least one element selected from the groupA consisting of Cr, Mo, W, Ge and Si.
 4. A magnetic recording medium forlongitudinal recording according to claim 1, wherein the nonmagneticmetallic underlayer comprises at least one metal element selected fromthe group consisting of Cr, Mo, W, V, Nb and Ta and at least one elementselected from the group consisting of Ti, Si, Ge, Cu, Pt, Rh, Ru, Re, Pdand oxygen.
 5. A magnetic recording medium for longitudinal recordingaccording to claim 1, wherein the first additive element is Pt, and thesecond additive element is Cr and Si.
 6. A magnetic recording medium forlongitudinal recording according to claim 4, wherein the first additiveelement is Pt and the second additive element is Cr and Si.
 7. Amagnetic recording medium for longitudinal recording according to claim1, wherein the magnetic layer of Co-based alloy has an inplanecoercivity of at least 1,200 Oe and a coercive squareness of S* of notmore than 0.85.
 8. A magnetic recording medium for longitudinalrecording according to claim 7, wherein the nonmagnetic metallicunderlayer has a thickness of 150 to 600 nm.